Benign leiomyomata (uterine fibroids) are common tumors which affect more than 25% of all women at some time during the reproductive years. Many women wish to have fibroid-related symptoms such as bleeding and pain treated without resort to hysterectomy. Pharmacologic therapy alone is of limited utility due to side-effects associated with long-term use. Hysteroscopic resection using the loop or vaporizing resectoscope is appropriate for those tumors which protrude into the uterine cavity--so called submucous myomas. Surgical myomectormy (removal of the fibroid) is often used for tumors which are thought to be the cause of infertility. However, this approach usually requires a laparotomy and is often associated with adhesion formation between the uterus, bowel and other adjacent structures. These adhesions can be the cause of chronic pain in some patients.
Needle myolysis is a promising technique whereby a laparoscope is used to introduce one or more needles into a fibroid tumor under visual control. Bipolar Radio Frequency ("RF") current is then delivered between two adjacent needles, or unipolar current between a single needle and a distant dispersive electrode affixed to the thigh or back. The aim of needle myolysis is to coagulate a significant volume of the tumor and thereby cause it to shrink substantially. The traditional technique is to make multiple passes through different areas of the tumor using the coagulating needle to destroy many cylindrical cores of abnormal tissue. However, the desirability of multiple passes is mitigated by the risk of adhesion formation, which is thought to increase with increasing amounts of injured uterine serosa, and by the operative time and skill required.
Recently, Goldrath and others have demonstrated that tumor shrinkage can be preferentially induced by destroying the tumor's blood supply, which is generally located on the periphery, rather than by targeting the bulk of the fibroid. Physicians acting on this observation use the needles to ring the tumor with cores of coagulation. This technique still calls for multiple tumor passes and, in the end, the operator remains uncertain as to the status of the tumor's blood supply.
Another problem with needle myolysis is the variability in generated lesion sizes created by the electrocautery generator. Electrosurgical lesions are created when radiofrequency current flows through tissue, resistively heating it to the point of cell death. It has been demonstrated in the RF catheter ablation literature and elsewhere that maximum energy transfer occurs when the electrode tissue interface temperature remains below 100.degree. C. Temperatures in excess of 100.degree. C. cause intracellular water to boil, desiccating tissue and reducing the electrical and thermal conductivity of the surrounding tissue. Under such conditions, the impedance seen by the ESU increases and current flow falls (since most ESUs are constant voltage sources). Since the electrocautery electrode itself acts as a passive heat sink, the highest tissue temperature is usually found at some depth from the tissue-electrode interface. Therefore, under ideal circumstances the coagulating electrode temperature would be maintained at some level below the critical 100.degree. C. temperature (e.g., 80.degree. C.).
Today, the surgeon must set ESU power levels based upon heuristics. However, the amount of energy required to maintain the tissue-electrode interface at the desired temperature will vary depending upon a number of factors, including the size of the coagulating needle, the blood flow in the surrounding tissue, etc. Excessive temperatures at the uterine serosa can be expected to increase the incidence of adhesion formation; this can lead to chronic pain in some patients.
To overcome the above limitations, it would be desirable to provide improved needle myolysis systems and methods to facilitate the accurate, controlled targeting of a tumor's blood supply. It would further be desirable if such an apparatus could provide feedback regarding the temperature at the tissue-electrode interface, and particularly the temperature of nearby tissues.